Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

New Job, New T1, New Routers, New Ip scheme - Need help

Here is the scenario

We have 2 LAN's connected via DSL modems over an ISDN line.

Just got 2 2620's with one ethernet and one serial interface. I want to roll over slowly to the new scheme as I have some apps to test and a new NT domain to create and I'd like to keep it all separate and add in hosts one at a time - meaning that I want it all be fully functional from both subnets until the old is phased out. There are no switches that would get in the way of my config. Hubs only.

I want to change the address scheme of my corporate LAN for several reasons - my main issue is that I am locked out of my ISDN modem and cannot give it a new address. The network is small (both LANs) and I think static routes are the way to go.

Here is my approach, though I am having some trouble with the implementation:

Create the new IP scheme to work with the T1, set the current Corp address scheme as a secondary bound to the same ethernet interface. When all is said and done (assuming I still haven't been able to change the ISDN modem ip), I want that secondary to only serve the internet connection.

But... I can't ping anything on the original subnet from within the router unless I reconfigure that local ethernet interface address as the primary ip.

Does a secondary address, which shows as directly connected with sh ip route, still require any static routes to get out? Or is the ping failing during the reply back?

I can ping both the ISDN modem and the secondary 2620 ethernet interface ( and, respectively) from the hosts on the network, as they are in the same broadcast domain.

I'm sure that I'm hanging up on something very fundmental here - thanks in advance for the help.


Re: New Job, New T1, New Routers, New Ip scheme - Need help

Often times complex configuration/troubleshooting issues are best addressed in an interactive session with one of our trained technical assistance engineers. While other forum users may be able to help, it’s often difficult to do so for this type of issue.

To utilize the resources at our Technical Assistance Center, please visit and to open a case with one of our TAC engineers, visit

If anyone else in the forum has some advice, please reply to this thread.

Thank you for posting.

Community Member

Re: New Job, New T1, New Routers, New Ip scheme - Need help

Did you ever get this working ? If you did not post the configs of the 2 routers.


Community Member

Re: New Job, New T1, New Routers, New Ip scheme - Need help

I am not sure I fully understand but I do know that the primary address is what shows up in the packet when you issue your ping which causes you to lose the packets. If you perform an extended ping and specify the source address it should work. If I understand the question correctly, no the router needs no static route for a directly connected subnet.

CreatePlease to create content